1. Field of Invention
The invention relates to television camera system for displaying on a television monitor images produced by transmission electron microscopes and particularly to systems that are positioned at the top of the microscope projection chamber.
2. Description of Prior Art
Transmission electron microscope (TEM) images are usually viewed on a fluorescent phosphor screen mounted at the base of the evacuuated microscope column. The images are of low intensity and must be viewed in a darkened room to carry out the precise focussing adjustments necessary before permanent recording of the image on photographic film. The relatively small size of the TEM viewing screen and the viewing windows make it impossible for more than two or three people to view the image at one time.
For these reasons, there is considerable interest in transferring the electron image to a television camera and displaying it on a TV monitor where it may be viewed simultaneously by many people in a lighted room and interfaced to a wide variety of electronic image processing and recording devices. the main design problem is to devise an efficient method of transferring the electron image formed inside the vacuum system to the TV camera mounted outside it.
Currently, there are two methods of coupling a television camera to the TEM. One uses a combination of lenses, mirrors and glass windows to transfer the light image, generated by a scintillator inside the microscope to a TV camera mounted outside. These lens coupled TV systems have been mounted both above and below the microscope viewing screen. Unfortunately, their poor light collection efficiency prevents them from producing clear images at the highest useful TEM magnifications and they cannot display the full resolution of the TEM.
The second approach uses a very thin transmission scintillator attached to a low loss fiber optic plate which in turn connects directly to the imaging face of a TV camera. The very low loss of direct coupling permits high resolution TEM images to be viewed easily at magnificationons up to .times.20 million on the TV monitor. However, the intimate contact required between the scintillator inside the vacuum and the TV camera outside is difficult to acheive and up to the present has only be obtained in systems mounted directly below the microscope viewing screen and solidly fixed to the base of the TEM projection chamber. The disadvantages of this arrangement is its incompatibility with other instrumentation, such as the electron energy loss spectrometer and other electron detectors which are normally mounted in the same position.
Most users, therefore, would find significant advantages in a camera system which produced good quality images and was compatible with other instruments mounted at the base of the TEM column.